To minimize the environment pollution,the biggest explosion workshop over the world is planned to construct.A deep investigation must be done in advance,especially on the natural ventilation.A 1/6 scale model is set to do experiment research.A 3D transient numerical simulation method is adopted to thoroughly study the attenuation of the toxic gas concentration under natural ventilation to full-scale and 1/6 scale models.Through the simulation,a scale constant of attenuation can be deducted between the 1/6 scale model and the full-scale model.With the experiment results of 1/6 model,the toxic gas exhaust time can be calculated to support the practical design in theory.